The Blancpain below is estimated to fetch between 30.000 and 40.000 US Dollars. For this, you’ll get a minute repeater, made out of platinum with a 21k gold rotor complete with box, papers and certificates!

Other auctionhouses are Antiquorum, Christies, Phillips-Auctions and ofcourse the online-only auctionhouse eBay. Although I doubt that eBay is a serious competitor for the other ones mentioned when it comes to very exclusive and expensive watches.